Bacteria Team Up to Wage Antibiotic War

Below:

Next story in Science

In the dog-eat-dog world of resource competition, a little
cooperation can go a long way toward ensuring victory for a
population of plants or animals. Now, researchers have found
humble bacteria work together for the common goal of survival,
too.

Ocean bacteria in the Vibrionaceae family
cooperate to compete against other Vibrionaceae strains,
biologists report Friday (Sept. 7) in the journal Science. Among
Vibrionaceae colonies, some individuals create powerful
antibiotics that kill outsiders, but not their own strain, the
researchers find. The discovery points to more complex social
interactions among wild bacteria than expected, and also reveals
a potential new source of antibiotics against human disease, said
study researcher Martin Polz, an environmental microbiologist at
the Massachusetts Institute of Technology.

"You have a few individuals within the population that take over
the role of the defender or the aggressor, if you will," Polz
told LiveScience. "Others are
resistant to the antibiotics produced by these individuals,
but they're not producing the antibiotics themselves."

Soldiering bacteria

The often-overlooked social lives of bacteria are extremely
important, Polz said, given that approximately 90 percent of the
ocean's biomass is microbial. Every milliliter of surface ocean
water contains about a million microbes, he said.

These microbes are responsible for producing nutrients, recycling
organic material and other basic processes that keep the oceans
humming along, Polz said. But little is known about how they
interact with one another.

To study these interactions, Polz and his colleagues use bacteria
from the Vibrionaceae, or Vibrio, family, which includes a number
of harmless
bioluminescent microbes as well as the bug that causes
cholera. In the lab, the researchers grew colonies of these ocean
bacteria and then pit colonies against one another to watch them
interact.

A look at 35,000 interactions between Vibrio colonies turned up
850 antagonistic clashes — the equivalent of bacterial warfare.
In statistically analyzing these fights, Polz and his colleagues
found that any given killer is more likely to kill outside of its
ecological population than within it.

"That was sort of the first cue that there is some structure
behind it," Polz said.

Antibiotic defenses

In fact, the researchers found, not every Vibrio individual
carries weight equally in battle. Some individual cells secrete
anti-intruder antibiotics that benefit the colony as a whole. In
some cases, these cells act like super-soldiers: About 5 percent
of individual Vibrio cells were capable of knocking out more than
25 percent of Vibrio strains from other colonies.

Polz compared these protective antibiotics with "public goods,"
an economics term used to describe resources like clean air or
national defense that benefit everyone in a society.

"In a sense, the nonproducers are
cheaters, because they don't have the cost of the production
[of antibiotics], but they benefit from this antibiotic," Polz
said. The system is stable anyway, he added, perhaps because
nonantibiotic-producers pull their weight in other ways, such as
producing enzymes or other molecules that the whole colony can
use.

This is the first time that such close cooperation has been
observed in natural bacterial populations, Polz said. (Most
laboratory bacterial studies involve bacteria with a common
cloned ancestor, meaning their genetic diversity is not as great
as in the wild.) As traditional antibiotics become increasingly
ineffective against antibiotic-resistant bacteria, ocean
antibiotic-producers may be a source for
new drugs, he added.

"This study demonstrates that there is a very large untapped
source of potential antibiotics out there in nature," Polz said.
"I think that looking into this in more depth will be very
important, because we face a rapid decline in the effectiveness
of current antibiotics."